Magnetic recording medium and method for manufacturing the same

Abstract

A fixed permanent pattern is used for identifying a magnetic recording medium and a high security against forgery or modification is obtained by a magnetic recording medium including a non-magnetic support and at least two magnetic layers formed on said support, characterized in that at least one of said at least two magnetic layers contains magnetic particles having a coercive force of 4,000 Oe or less dispersed in a binder and has a non-rewritable fixed signal which has been recorded by magnetic field generated by a signal recorded on one or more other magnetic layers under the influence of an orientation magnetic field.

What we claim is: 
     
       1. A magnetic recording medium including a non-magnetic support and at least two magnetic layers formed on said support, characterized in that said at least two magnetic layers includes a first magnetic layer on said support and a second magnetic layer above said first magnetic layer containing magnetic particles having a coercive force of 4,000 Oe or less dispersed in a binder and has a non-rewritable fixed signal which has been recorded by a magnetic field generated by a signal recorded on said first magnetic layer under the influence of an orientation magnetic field having a magnetic field strength lower than the coercive force of said first magnetic layer but strong enough to cause the movement of said magnetic particles. 
     
     
       2. A magnetic recording medium according to claim 1, wherein said non-rewritable fixed signal recorded on said second magnetic layer is formed by specific areas and other areas adjacent to said specific areas, said specific areas have a different magnetic output per unit area from said other areas. 
     
     
       3. A magnetic recording medium according to claim 2, wherein said non-rewritable fixed signal recorded on said at least one magnetic layer is an information for identifying the magnetic recording medium. 
     
     
       4. A magnetic recording medium according to claim 1, wherein said non-rewritable fixed signal recorded on said second magnetic layer is formed by specific areas and other areas adjacent to said specific areas, said specific areas have a different number of magnetic particles per unit volume from said other areas. 
     
     
       5. A magnetic recording medium according to claim 4, wherein said non-rewritable fixed signal recorded on said at least one magnetic layer is an information for identifying the magnetic recording medium. 
     
     
       6. A magnetic recording medium according to claim 1, wherein said non-rewritable fixed signal recorded on said second magnetic layer is an information for identifying the magnetic recording medium. 
     
     
       7. A method for manufacturing a magnetic recording medium including a non-magnetic support and at least two magnetic layers formed on said support, which comprises the steps of forming a first magnetic layer on said non-magnetic support;   magnetically recording a specific signal on said first magnetic layer;   applying a magnetic coating on a surface of said first magnetic layer to form a second magnetic layer which contains magnetic particles having a coercive force of 4,000 Oe or less dispersed in a binder;   applying a magnetic orientation field having a field strength lower than the coercive force of said first magnetic layer but strong enough to cause the movement of said magnetic particles to said magnetic coating prior to completion of drying and solidification of said magnetic coating;   and performing said drying and solidifying of said magnetic coating to form said second magnetic layer which has a non-rewritable fixed signal which has been recorded by the magnetic field generated by said signal recorded on said first magnetic layer under the influence of said magnetic orientation field.   
     
     
       8. A method for manufacturing a magnetic recording medium according to claim 7, wherein said magnetic orientation field applied to the magnetic coating for the second magnetic layer prior to the drying and solidification of said magnetic coating is substantially uniform along the surface of said first magnetic layer. 
     
     
       9. A method for manufacturing a magnetic recording medium according to claim 8, wherein said magnetic orientation field is generated by magnetic orientation means, said drying and solidification were effected by drying means, and at least a part of said magnetic orientation means is located in said drying means. 
     
     
       10. A method for manufacturing a magnetic recording medium according to claim 7, wherein said magnetic orientation field is generated by magnetic orientation means, said drying and solidification were effected by drying means, and at least a part of said magnetic orientation means is located in said drying means. 
     
     
       11. A method for manufacturing a magnetic recording medium according to claim 8, wherein said magnetic orientation field is generated by magnetic orientation means including a solenoid coil. 
     
     
       12. A method for manufacturing a magnetic recording medium according to claim 10, wherein said magnetic orientation field is generated by magnetic orientation means including a solenoid coil. 
     
     
       13. A method for manufacturing a recording medium including a non-magnetic support and at least two magnetic layers formed on said support, which comprises the steps of forming a first magnetic layer on said non-magnetic support;   magnetically recording a specific signal to said first magnetic layer;   applying a magnetic coating on a surface of said first magnetic layer to form a second magnetic layer contains magnetic particles having a coercive force of 4,000 Oe or less dispersed in a binder;   applying a DC magnetic orientation field having a field strength lower than the coercive force of said first magnetic layer to said magnetic coating simultaneously with application of said magnetic coating on the surface of said first magnetic layer;   and thereafter drying and solidifying said magnetic coating to form said second magnetic layer which has a non-rewritable fixed signal which has been recorded by the magnetic field generated by said signal recorded on said first magnetic layer under the influence of said magnetic orientation field.   
     
     
       14. A method for manufacturing a magnetic recording medium according to claim 13, wherein said DC magnetic orientation field applied to the magnetic coating for the second magnetic layer simultaneously with the application of said magnetic coating is substantially uniform along the surface of said first magnetic layer. 
     
     
       15. A method for manufacturing a magnetic recording medium according to claim 14, wherein said method further comprises a step of applying a second DC magnetic orientation field after the application of said magnetic coating but prior to completion of said drying and solidification. 
     
     
       16. A method for manufacturing a magnetic recording medium according to claim 14, wherein said DC magnetic orientation field is generated by a DC solenoid coil. 
     
     
       17. A method for manufacturing a magnetic recording medium according to claim 16, wherein said method further comprises a step of applying a second DC magnetic orientation field after the application of said magnetic coating but prior to completion of said drying and solidification. 
     
     
       18. A method for manufacturing a magnetic recording medium according to claim 13, wherein said method further comprises a step of applying a second DC magnetic orientation field after the application of said magnetic coating but prior to completion of said drying and solidification. 
     
     
       19. A method for manufacturing a magnetic recording medium according to claim 19, wherein said second DC magnetic orientation means is substantially uniform along the surface of the first magnetic layer. 
     
     
       20. A method for manufacturing a magnetic recording medium according to claim 18, wherein said second DC magnetic orientation means is generated by a DC solenoid coil.